View of /trunk/vfw/help.txt

xvid vfw help
20/jan/02
*** rate control ***
xvid offers a number of different rate control modes
- 1pass-cbr: constant-bitrate
use the bitrate slider to select the desired bitrate; refer to 'cbr constants' for advanced options. note: we actually use an average-bitrate algorithm, so the instaneous bitrate will fluxuate.
- 1pass-quality
use the quality slider to select a desired quality percentile. the quality% is then used to calculate an average-quantizer.
- 1pass-quantizer
force the codec to use a fixed quantizer for all frames. valid range: [1,31].
- 2pass
a detailed explaination of 2pass can be found here: http://www.research.ibm.com/journal/rd/434/westerink.html
our implementation of two pass encoding requires three steps
1) 1stpass: collect compression statisics to a stats file.
2) process the stats using gordian knot, xihprom, etc.
3) 2ndpass: compress the video using both the original 1stpass stats file, and the normalized stats file.
*** encoder tuning ***
- max keyframe interval
the maximum interval between keyframes.
- motion search precision
controls the speed/quality of the motion search algorithm. range [0,6].
lower values are faster but reduce compressibility.
higher values are slower but increase compressibility.
- quantization type
quantization is the process of removing detail. there are two types:
h.263: used by divx4.x and h263 encoders.
mpeg: used by the microsoft mpeg-4 encoder, mpeg-1/2.
mpeg quantization gives sharper looking images, but can introduce grain/noise. while h.263 gives softer looking images, removes noise (but sometimes too much) and is slightly faster.
*** cbr constants ***
these apply only to 1pass-cbr mode.
- average peroid
the number of frames over which the average bitrate is maintained.
- reaction peroid
(?) the number of frames inwhich we react to sudden change in bitrate.
- up/down ratio
(?) a percentile representing how fast/much we react.
*** debug ***
- min/max quantizer.
lets you limit the flexibility of the encoder.
a minquant=1 can sometimes cause problems with 1pass-cbr and 2pass.
- luminance masking
enabled per-macroblock quantizer decision. very experimental
- discard encoded bitstream on 1st-pass
by default xvid discards the compressed bitstream during the the 1st pass of a two pass encoding session. example: in windows you end up with an empty .avi file. if this box is unchecked the bitstream is kept.
note: the 1st compressed bitstream can large.
this can be used to perform a 'fast 2pass' encoding.
1) perform 1st pass encoding of your source material with discard unchecked.
2) process the stats file
3) open the bitstream created in the first pass, and perform the 2nd pass on it.
note: there is some quality loss. judge it for yourself.
- perform dummy 2nd-pass
this can be used to check the accuracy of your stats file processor/calculator. it instructs xvid to create a dummy/junk bitstream exactly to the size described in the processed stats file.
*** cpu ***
provides auto/manual control over cpu-feature optimizations.
*** about ***
build timestamp, etc.